Integrally molded plastic fastening elements of the type disclosed in U.S. Pat. No. 3,651,734, issued to the present inventor on March 28, 1972, are rapidly gaining commercial acceptance, both here and abroad. These fastening elements comprise, in substance, a head for disposition at one end of an opening, expansible locking means for location at the other end of the opening, and flexible, spaced apart connectors extending therebetween.
More specifically, the above prior art fastening elements typically utilize relatively long connectors which extend radially outward far beyond the edges of the opening when the fastening element is in its expanded, locking position. The locking means typically comprises a pair of toggle members pivotally connected together at their adjacent ends so that they are moveable between a collapsed position in which they can be inserted through an opening and an expanded position in which they secure the fastener within the opening. The connectors are joined to the toggle members at locations on the toggle members such that when the toggle members are moved into the expanded position, the connectors are forced apart relatively far from their conformation in the collapsed condition so that they extend radially outward far beyond the edges of the opening. In this structure, much of the load on the fastening element is borne by the relatively long, relatively flexible connector elements.
While the aforesaid fastening elements have proven to be highly satisfactory in a wide variety of applications, the present invention is directed to devices having features particularly useful in applications requiring high load-bearing capability.